Like Pearls in the Sky

The only known supernova remnant of its kind in the Milky Way has an unexpectedly intricate structure: chains of gas knots resembling pearls on a string, each wide enough to fit the solar system multiple times. Using the Gemini North telescope, an international team co-led by Ilaria Caiazzo, assistant professor at the Institute of Science and Technology Austria (ISTA), captured the most detailed view yet of Pa 30, revealing striking new features of a remnant associated with a historical supernova witnessed nearly 850 years ago. The findings were published in The Astrophysical Journal.

Is this a fireworks display? Described as a dandelion-shaped remnant of a massive stellar explosion, this object shows us the aftermath of the blast. Adding to its unusual character is a surviving ‘zombie star’ at its core—the stellar remnant of an incomplete explosion.

First identified in 2013 by a citizen scientist, the supernova remnant nebula Pa 30 was later linked to a historical stellar explosion witnessed and recorded independently in Japanese, Chinese, and Arabic historical sources in 1181. This has connected Pa 30 to one of just five supernovae recorded before the telescope era whose remnants had long remained unidentified.

Using NOIRLab’s Gemini North telescope, an international team of astronomers co-led by Tim Cunningham from the Center for Astrophysics | Harvard & Smithsonian and Ilaria Caiazzo, assistant professor at the Institute of Science and Technology Austria (ISTA), has now revealed the most detailed view yet of Pa 30. Their findings: What appeared to be smooth ‘firework’ streaks are actually chains of knots resembling pearls on a string—each wide enough to fit ten times Neptune’s orbit, the planet furthest out in our solar system, with room to spare.

Only known example in our galaxy

At about 7,500 light-years away, Pa 30 is relatively close to Earth by astronomical standards; much nearer than the center of the Milky Way, about 26,000 light-years away. Although these distances sound very large, they are quite small compared with the immense scale of the Universe.

Pa 30 is the only known object of its kind in the Milky Way. While astronomers have identified a few similar objects in other galaxies, it remains the only one where our telescopes can see the surviving remnant of the incomplete explosion at its core—the ‘zombie star.’ This type of incomplete explosion is known as a Type Iax supernova, a rare class of stellar explosion. Researchers have proposed that Pa 30 resulted from a collision between two white dwarfs—extremely dense, Earth-sized stellar remnants that have exhausted their fuel and shed their outer layer.

“We can see this much detail because of Pa 30’s proximity to Earth,” says Caiazzo. “This proximity makes Pa 30 uniquely valuable for study.”

Rare but no anomaly?

According to Cunningham, our galaxy could also be home to other remnants of Type Iax supernovae that have yet to be spotted.

“Reliable historical records of stellar explosions extend back only about a thousand years. For all we know, there might well be similar remnants still lurking in the dark in our own galaxy,” he says. “Today, we are lucky to study an intriguing object we know was observed by astronomers who made three independent historical records of the event centuries before the invention of the telescope.”

Although Type Iax supernovae are rare, the team does not consider it surprising that Pa 30 was identified as one.

“We will likely identify more similar objects as new telescopes continue to inspect the depths of our night sky,” adds Cunningham, who is now an assistant professor at the University of Warwick, UK.

Like pearls on a string

The team analyzed ionized sulfur (S II) emission lines in the red part of the visible light spectrum and doubly ionized oxygen (O III) emission, shown in blue-green tones. The S II observations revealed roughly ten times as many filamentary features as previous images could resolve. The data also show that Pa 30’s filaments are composed of tight chains of gas knots that appear to have remarkably uniform sizes.

“The planetary region of our solar system could fit in each knot about ten times with room to spare,” says Caiazzo. “The knots are quite strikingly uniform. We are excited to try to model them.”

The team also found that the surviving zombie star seemed to sit almost perfectly in the nebula’s center. In many supernovae, an asymmetric explosion gives any surviving star a ‘kick,’ sending it away from the explosion center.

“Explosions conserve momentum. If the explosion itself was perfectly symmetric, the ejecta should also be symmetric, and the surviving star should not receive a substantial kick,” says Caiazzo. “We were able to measure a precise upper limit of the remnant star’s transverse kick speed, showing that it was surprisingly small. We practically don’t see the star moving away at all.”

Premier astronomical observation site

For these new observations, the team used the Gemini North telescope on Mauna Kea in Hawai’i, situated at an elevation of more than 4,200 meters. Gemini North is one half of the International Gemini Observatory, with its twin telescope, Gemini South, located in Chile. It is partly funded by the U.S. National Science Foundation (NSF) and run by NSF NOIRLab. The telescope’s capabilities, coupled with its location in one of the world’s premier astronomical observation sites, enabled the team to achieve the best-resolution images and analysis of Pa 30 to date.

Many questions about Pa 30 remain and these observations may help astronomers identify similar remnants elsewhere.

“Astronomy has entered the big data era,” says Cunningham. “Our findings will help us screen through the enormous datasets.”

Caiazzo adds, “In general, the farther into space we look, the more difficult it is to detect faint signals and interpret them. While we can see Type Iax supernovae in distant galaxies as point sources of light, resolving the remnants of such explosions is only possible in our own galaxy and in very few nearby ones. Eventually, we plan to use Pa 30’s distinctive properties to search the Milky Way and nearby galaxies for similar objects.”

Link to the NOIRLab release: https://noirlab.edu/public/news/noirlab2624/

Publication:

T. Cunningham, I. Caiazzo, J. C. Raymond, and S. J. Kenyon. 2026. Detection of knots in the supernova type Iax remnant Pa 30. The Astrophysical Journal. DOI: 10.3847/1538-4357/ae9cb2

Funding information:

This project was supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51527.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.